Reaction Kinetics of the Invertase from Yeast (S. Cerevisiae)

Invertase converts sucrose to glucose and fructose. The reaction mechanism for the formation of glucose and fructose was studied by stopped flow spectrophotometer and circular dichroism. The reaction mechanism follows biphasic mode with rate constants of k₁0.0053 s^?1?±?0.001 s^?1 and k₂ 0.030 s^?1?±?0.01 s^?1 for 25 mM concentration of sucrose. Far UV circular dichroic spectrum of invertase in presence of sucrose shows 18 % increase in β conformation as a function of time. Taken together, the invertase hydrolysis follows biphasic mode where it undergoes conformational changes followed by hydrolysis of the sucrose.     

Testing the Mean Vector and the Correlation Coefficient in Life-Testing Under Bivariate Normality

In life-testing situations under bivariate normality of (X, U), a few smallest or a few largest Y-observations may not be available. Tests for μ = 0 (mean vector) and o = 0 (correlation coefficient) are developed from the available Y-observations and their concomitant X-observations. The robustness of these tests to departures from normality is investigated.     

Production of hydrogen peroxide by rabbit articular chondrocytes. Enhancement by cytokines

Recent evidence suggests that reactive oxygen intermediates may play a role in the etiology of cartilage matrix degradation in arthritis. We have previously established that normal articular chondrocytes can functionally act as macrophages. These functions include expression of class II MHC Ag, presentation of Ag and induction of mixed and autologous lymphocyte stimulation. Inasmuch as the production of reactive oxygen intermediates is a hallmark of macrophage activity during inflammatory response, we were interested in examining the ability of normal articular chondrocytes to produce reactive oxygen intermediates. Using the trapped indicator 2',7'-dichlorofluorescin diacetate (DCFH-DA), we measured the levels of intracellular hydrogen peroxide within normal rabbit articular chondrocytes. We found that Concanavalin A induces chondrocytes to rapidly oxidize 2',7'-dichlorofluorescin diacetate to a highly fluorescent dichlorofluorescin in a dose- and time-dependent manner. Fluorescent dichlorofluorescin oxidation by chondrocytes was inhibited by the addition of catalase, an enzyme that detoxifies hydrogen peroxide. Exposure of rabbit chondrocytes to either IFN-gamma or TNF primed the chondrocytes to produce significantly greater amounts of hydrogen peroxide with or without further stimulation. Using scopoletin oxidation as a measure of the release of hydrogen peroxide, we confirmed that chondrocytes released this reactive oxygen intermediate after adherence to serum coated culture plates. Rabbit articular chondrocytes produced and released greater amounts of hydrogen peroxide than pulmonary alveolar macrophages, a well characterized macrophage cell type. These observations suggest that chondrocytes are an important source of reactive oxygen intermediates. Furthermore, the production of reactive oxygen intermediates by chondrocytes may be an important mechanism by which chondrocytes induce structural and functional alterations in cartilage matrix observed during arthritis.     

Logistic and Nonlogistic Density Functions in Binary Regression with Nonstochastic Covariates

A binary random variable depends on nonstochastic covariates through a density function. The equations that determine the maximum likelihood estimators of the parameters are intractable and difficult to solve iteratively. We develop modified maximum likelihood estimators for both logistic and nonlo-gistic densities. These estimators are explicit functions of sample observations and are, therefore, easy to compute. They are asymptotically fully efficient and, for small samples, are almost fully efficient. The appropriateness of the logistic density function is also discussed.